A carbon material (fullerene soot) having a nanometer-sized microstructure is contained in soot prepared by vaporizing carbon by arc discharge using graphite electrodes or laser irradiation to carbon in an inert atmosphere, and allowing the vaporized carbon to aggregate through gradual cooling. As the configuration of fullerene soot, a single-wall sphere represented by C60, a multiwall sphere having a small void formed therein (carbon nanoparticle), a single-wall tube contained in soot prepared by vaporizing carbon by an arc discharge using graphite in which a specific metal catalyst is mixed (single-wall carbon nanotube), and a multiwall tube in which several single-wall nanotubes are concentrically arranged (multiwall carbon nanotube: deposited on the surface of the cathode when using graphite in which a metal catalyst is not mixed) have been known.
These carbon materials are expected to find applications in new material fields. As a technology of producing these carbon materials, JP-A-2001-48508 discloses a method which includes applying a high-energy beam such as electron beams, γ-rays, or X-rays to carbon soot prepared by incomplete combustion or pyrolysis of a carbon-containing compound such as a hydrocarbon or an aromatic oil to obtain nanometer-sized graphite spheres, and JP-A-2001-64004 discloses a method which includes applying laser light to a solid carbon material such as sintered carbon in an inert gas atmosphere to vaporize carbon, suspending and dispersing the resulting soot-like material in a solvent, and collecting individual or aggregated spherical particles to obtain single-wall carbon nanohorns. JP-A-2003-206120 discloses a method which includes applying a carbon dioxide laser beam to carbon in an inert gas atmosphere at 5 to 10 atm to produce cluster carbon heated to 1000° C. or more to obtain nanographite spheres.
A material obtained by the above methods has a solid structure or a structure having minute voids formed therein, and is expected to be applied as a light-absorbing material, an ultrahard material, a hydrogen storage material, a methane gas storage material, a gas reforming material, an abrasive, a lubricant, and other new functional materials. On the other hand, if a nanometer-sized hollow carbon structure having a larger inner space can be obtained, such a structure can be applied to a wider range of product fields due to the structural feature of having a graphite outer shell and a hollow inner space.
As a method of producing a nanometer-sized hollow carbon structure, JP-A-2000-344506 discloses a method of producing a carbon nanocapsule containing a metal particle by bringing a gas mixture containing carbon dioxide and hydrogen into contact with a transition metal catalyst containing metal particles at a reaction temperature of 450 to 750° C. to subject carbon dioxide to catalytic reduction, and JP-A-2003-81619 discloses a method of producing a carbon nanocapsule with an outer diameter of 100 nm or more by supplying a raw material gas containing carbon to a glow discharge plasma generated by microwaves to decompose the raw material gas. The carbon nanocapsule obtained by the former method contains a metal in the hollow space, and the carbon nanocapsule obtained by the latter method contains a Co particle and is used to produce a recording medium by causing the nanocapsule to adhere to a disc or to confine a luminescent material or an optical material. These carbon nanocapsules do not have a completely closed space. A carbon polyhedron having a polyhedral structure in which several to several tens of graphite sheets are nested may be obtained by arc discharge (see Chem. Phys. Lett. 204. 227 (1993)). Since the carbon polyhedron does not necessarily have a hollow inner space and has a relatively small particle diameter ranging from several to several tens of nanometers, a number of substances cannot be provided in the carbon polyhedron. Specifically, a method of efficiently and stably obtaining a nanometer-sized hollow carbon structure having a large inner space has not yet been put into practice.